Seawater carbonate chemistry and phytoplankton biomass during the BIOACID II indoor mesocosm study in the Kiel Fjord (Baltic Sea)

• Main Authors: Paul, Allanah Joy, Sommer, Ulrich, Paul, Carolin, Riebesell, Ulf
• Format: Dataset
• Language: English
• Published: PANGAEA 2018
• Subjects: Alkalinity; total; Aragonite saturation state; Baltic Sea; Bicarbonate ion; Biomass/Abundance/Elemental composition; Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; Community composition and diversity; DATE/TIME; Day of experiment; Dolichospermum spp.; biomass; Entire community; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Laboratory experiment; Mesocosm label; Mesocosm or benthocosm; Nodularia spp.; Nostoc sp.; biomass as carbon; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Phase; Phosphate; organic; Phytoplankton; Ratio; Salinity; Sample code/label; Silicate; Temperate; Temperature; water; Treatment: temperature; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.901801; https://doi.org/10.1594/PANGAEA.901801

Nitrogen fixation is a key source of nitrogen in the Baltic Sea which counteracts nitrogen loss processes in the deep anoxic basins. Laboratory and field studies have indicated that single-strain nitrogen-fixing (diazotrophic) cyanobacteria from the Baltic Sea are sensitive to ocean acidification and warming, 2 drivers of marked future change in the marine environment. Here, we enclosed a natural plankton community in 12 indoor mesocosms (volume 1400 l) and manipulated partial pressure of carbon dioxide ( pCO2) in seawater to yield 6 CO2 treatments with 2 different temperature treatments (16.6°C and 22.4°C, pCO2 range = 360-2030 µatm). We followed the filamentous, heterocystous diazotrophic cyanobacteria community (Nostocales, primarily Nodularia spumigena) over 4 wk. Our results indicate that heterocystous diazotrophic cyanobacteria may become less competitive in natural plankton communities under ocean acidification. Elevated CO2 had a negative impact on Nodularia sp. biomass, which was exacerbated by warming. Our results imply that Nodularia sp. may contribute less to new nitrogen inputs in the Baltic Sea in the future.